Squirting press for thermoplastic masses



Sept. 29, 1942. E. HEMPEL 2,297,474

I SQUIRTING PRESS FOR THERMOPLASTIC MASSES Filed June 20, 19:56 3 Sheets-Sheet 1 Fig.4

l I u Sept. 29, 1942. E. HEMPEL SQUIRTING PRESS FOR THERMOPLASTIC MASSES Filed June. 20, 1936 3 Sheets-Sheet 2 3 TORNEYS.

3 Sheets-Sheet 3 E. HEMPEL SQUIRTING PRESS FOR THERMOPLASTIC MASSES Filed June 20, 1936 Sept. 29, 1942.

Patented Sept. 29, 1942 UNITED STATES PATENT OFFlC SQUIBTING PRESS FOR THERMOPLASTIC MASSES Emil Hempel, Zerbst, Germany; vested in the Alien Property Custodian Application June 20, 1936, Serial No. 86,402 In Germany June 29, 1935 16 Claims.

The present invention consists in a machine which itself takes over the task of producing the correct operating conditions. In order to prevent the working material from being squirted out too quickly and to allow suflicient time for heating the squirted material so that it will be sufliciently plastic, a pressure gauge is connected up to the squirting piston, the said pressure 20 gauge adjusting 2. preferably hydraulic brake connected to the driving piston, according to the resistance of the squirted substance, when the resistance for any reason exceeds the maximum pressure permissible for the moulded article, which has been previously determined by experiment and for which, the adjustment has been eiiected. In this manner,'the operating speed of the squirting piston is reduced from a selected squirting pressure by retarding the forward movement of the driving piston to correspond to the resistance. It is thus ensured that the squirting of the mass will be effected in a regulated manner, one, object of which is to provide for suflicient heating of the mass. This is for instance attained by a weight-loaded wedge slide which is adjusted by the pressure fluid of a measuring gauge fitted in the squirting piston, proportionately to the pressure in the measuring gauge, the said wedge slide in turn adjusting a control valve in the circulation pipe of the hydraulic brake in such a manner that the cross section of the opening through the valve is correspondingly reduced, if need be until the valve is fully closed. The action of the wedge slide can be adjusted, in the first place by varying the loading weight acting against the pressure of the fluid in the measuring gauge and then by varying the leverage with which the loading weight acts. More particularly, the counterweight may be suspended from a snail plate which is adjustable relatively to the wedge slide.

The hydraulic brake for regulating the operating speed of the driving piston is, in accordance with the invention, connected up to a second hydraulic brake, which comes into action during the return stroke of the driving piston, at the end of the stroke, in that it reduces the velocity of the return movement of the driving piston at the end of the return stroke, whereby the driving piston is prevented from coming to a stop with a blow at stroke.

For obtaining the same effect as the features above referred to, namely the automatic production of the correct operative conditions by the machine, a new form of drive is provided. This new form of drive is characterised by the feature that a toggle is interposed between the driving piston and the press or squirting piston, which depresses the squirting piston-rapidly at the commenceni-ent of the forward movement of the driving piston and later in the course the forward movement of the driving piston depresses the squirting piston more slowly.

It'is known to drive such machines on the one hand hydraulically or pneumatically by means of a press piston movable in a cylinder or by means of a toggle actuated by a crank. In the case where the drive is effected by means of a pressure medium, however, a toggle has not hitherto been interposed because its use has not been considered necessary. The pressure of the pressure fluid has simply been allowed to act directly to a 'sumcient extent to enable the necessary press pressure to be obtained. By this means, however, when the thermoplastic mass is ver viscous, very considerable pressures are developed, so that compressors or compressing pumps operating at very high pressures are necessary and the supply piping to the squirting machine has to be constructed to withstand very high pressures.- This results not only in the manufacturing costs of the machine plant being considerably higher but also in the operation and maintenance of the machine being rendered diflicult. Should leakage occur, then such leakage is more troublesome the higher thepressure In contradistinction thereto, the driving piston in the arrangement according to the invention can be operated with a pressure fluid at a comparatively low pressure. A few atmospheres suflice because the toggle produces the necessary pressure step up. The toggle, however, is an exceedingly simple machine element which is easily kept in repair and cheap, its interposition between the pressurefluid piston and the squirting piston re- I ducing the cost of the entire plant, simplifying its operation and rendering it reliable. All these advantages disappear if the machines are operthe end of the return ated with crank drive and toggle, even though the'pressure step up per se is also present.

In addition to these advantages, the provision of the toggle has the advantage that the squirting pressure is greatest when the squirting is taking place. The mass which has been charged into the press cylinder is at the outset granular and loosely layered and passes into a viscous state under the influence of the pressure and heat which is supplied from the outside; while the mass is still granular, a lower pressure suffices, if only to avoid premature extrusion of the mass out of the press cylinder into the mould.

On the other hand, when the mass has become viscous under the pressure and heating and has now in fact to be expelled, a very much greater pressure is required. This requirement is attended to by the toggle itself.

Finally, the invention comprises a special construction of toggle mechanism in which the guide. lever of the toggle is pivoted on a swinging lever which by means of a linkage transmits the force acting on the guide rod of the toggle to the mould with a considerable step up. By this means the advantage is obtained that the peak pressure exerted by the toggle is utilised at the same time to maintain the mould closed, the pressure required for maintaining the mould closed being always greater than the pressure exerted by the contents of the mould which tends to open the mould. x

A constructional example of a squirting machine according to the invention is illustrated i the drawings, in which Fig. 1 is a side elevation of the machine, partly in section,

Fig. 2 is a vertical section of the squirting piston with the guiding means and actuating mechanism, I

Fig. 3 is a side elevation of the parts shown in Fig. 2..

' Referring to the drawings, it is pointed out at the outset that the braking mechanism of the driving piston and its loading weights are shown in alternative positions in Figs. 1, 2 and 3. This is in order to render the illustration clear. In practice, each of the three alternative positions of these parts shown. in the individual figures is possible. All the three representations of these parts agree in form and the number of their members with one another.

The squirting piston 2 is movable vertically in a guide 3 on the machine frame I. Below the squirting piston lies the two-part mould 4.

' The cylinderi, for instance a compressed air cylinder, serves for the drive of the squirting piston, a piston 6 being slidable in the said cylinder the' said piston in the illustrated example being constructed as a differential piston, the larger side of which produces the working pressure and thesmaller side serves for returning the working and squirting pistons. The piston 6 tainer l3 for receiving the squirted material and into which the lower end of the squirting piston extends. .The container I3 has an outlet l5 which as shown in Fig. 1 rests directly upon the squirting mould, the bore of the container forming 'a-continuation of a bore in the squirting mould.

Laterally of the container 3 is located a filling device l6 for the squirted material which is supplied from the filling-device by means of a measuring roller I! to the filling cylinder l3.

.The mould 4 restsupon a platform l9 which can be raised and lowered through the intermediary of a screw spindle IS, a nut and toothed reduction gearing 2| by a small electric motor which is automatically switched on and off by means of.contacts controlled by the machine. In this manner the motor can close and open the .mould.

The squirting piston, as shown in Fig. 2, is constructed in two parts, comprising a sleeve 23 and a squirting piston' proper 24 which is axially Y slidable in this sleeve. The piston 24 is packed with respect to the sleeve 23 at 25 .and 26 and the hollow space 21 above the piston 24 is filled with oil, a flexible pipe 29 leading from the hollow space 2'! to the control means for adjusting-the piston velocity,

The said control means comprises a small piston 29 which extends into the tube 28 and is rigidly connected to a wedge slide 30, which is in part provided with gear teeth which engage in a gear wheel 3|, on the spindle 32 of which a snail plate 33 is fixed. Around the snail plate 33, which is enclosed in a casing 34, is passed a tension member, e. g. a chain 35 on which hangs a composite weight 36 serving for maintaining the pressure of the liquid from the space 21 act- .ing on the small piston 29 of the weighing device. The opposing pressure acting on the piston 29 can be varied by adjusting the snail plate 33 relatively to the gear wheel 3|, which is connected to the spindle 32 by means of a coupling 31, which, can be opened and closed by means of a hand wheel 38. When the coupling is opened the gear wheel 3| and the snail plate 33 can be turned relatively to one another. In this manner the lever arm at which the weight 36 acts. can be varied.

A brake piston 39 is connected to the working piston 6, the said brake piston being slidable in two cylinders 40 and 4|. The cylinder 40 serves as brake cylinder during'the working stroke,

while the cylinder 4| serves as brake cylinder at the end of the return stroke. Both cylinders are filled with oil. To the cylinder 49 belongs a circulating pipe 42 in which a valve 43 is interposed, thevalve body 44 of which rests upon the wedge surface 45 of the wedge'slide 30. The position of the valvebody 44 varies according to the position of the slide 30 and with it the braking resistance which the oil, forced by the piston 39 through the circulating pipe 42, exerts upon the working piston 6. A second circulating pipe 46 with a brake valve 4'! belongs to the cylinder 4|. The valve 41 produces the braking pressure during the return of the piston 6.

It has already been mentioned that the lower pivot 2 of the uide lever 9 does not have a fixed location, the lever onthe contrary being pivoted on a two-armed lever 48 which is capable of rocking about a fixed fulcrum 49 on the machine. The free end of the lever 48 rests upon a pressure rod 5| which bears against a onearmed lever 52 capable of rocking about a fulcrum socket 53 in the machine frame, the lever also bearing with its back 54 upon a sleeve 55' The mode of operation of the machine described is as follows:

After the mould 4 has been inserted and closed by means of the motor 22 and the spindle IS, the container I3 is filled with material to be squirted. A pressure medium, e. g. compressed air is then admitted to the cylinder 6, whereupon the piston 2 is forced downwardly through the intermediary of the toggle 9, It. By this means, the plastic mass I 4, which is heated by any suitable means, is compressed and finally forced through the bore of the outlet l5 into the press mould 4.

Under the reaction pressure of the inner part 24 of the squirting piston 2 acting on the fluid in the space 21, fluid is forced out of this space into the pipe 28. This fluid in turn exerts pressure upon the piston 29 and the latter displaces the wedge slide 30 outwardly against the load produced by the weight 36. By this means, the weight 36 is always adjusted into a new position of equilibrium according to the resistance of the plastic mass and the opposing pressure of the weight 36 which is varied bythe snail plate 33, that is to say, as the resistance rises, the further movement of the toggle causes the valve body 44 of the oil brake of the driving piston 6 to rise, thereby gradually increasing the oil resistance in the circulation pipe 42, so that as the resistance of the squirted material rises theworking piston 6 moves progressively more slowly. This is important in order to give the viscous plastic mass time to flow out into the mould and thereby prevent overloading of the machine.

On the return stroke of the working piston i, the oil brake 39, 4| comes into action and absorbs any blow which might be set up during the return travel of the piston. The length of the cylinders 40 and 4| determines the times when the oil brake comes into action during the forward and return movements of the working piston 6.

When the toggle 9, l0, increases the press pressure acting on the squirted material, then the force with which the guide rod 9 of the toggle acts upon the two-armed lever 48 and consequently also the pressure of the rod 5| acting on the one-armed lever 54 also increases. The lengths of the levers 48 and 52 are so proportioned that the closure pressure of the squirting mould is always greater than the opening pressure which the plastic mass injected into the mould exerts outwardly on the mould. In this manner, the mould is always held closed. On the other hand, it is automatically relieved of load when the toggle is drawn back.

What I claim is:

1. In a machine for squirting thermoplastic masses, in combination a driving piston, a squirting piston operatively connected to said driving piston for actuation by the driving piston, a brake operatively connected to the driving piston for retarding the motion of the driving piston during the working stroke and adjusting means for said brake including a pressure-responsive device connected to the squirting piston for adjusting the braking resistance, so as to increase the braking resistance as the squirting resistance rises and retard the forward movement of the driving piston and squirting pistons to correspond to the increasing resistance set up by the thermoplastic mass as the squirting progresses.

2. In a machine for squirting thermoplastic masses, in combination a driving piston, a squirting piston operatively connected to said driving piston for actuation by the driving piston, a fluid pressure brake operatively connected to the driving piston for retarding the motion of the driving piston during the working stroke and ad- Justing means for said brake including a pressure-responsive device connected to the squirting piston for adjusting the braking resistance, so as to increase the braking resistance as the squirting resistance rises and retard the forward movement of the driving piston and squirting pistons to correspond to the increasing resistance set up by the thermoplastic mass as the squirting progresses.

3. In a machine for squirting thermoplastic masses, in combination a driving piston, a squirting piston operatively connected to said driving piston for actuation by the driving piston, a fluid pressure brake operatively connected to the drivtion pipe for said brake having a control valve therein for permitting the escape of fluid into the circulation pipe to reduce the braking action, adjusting means for said valve including a wedge slide and a pressure responsive device connected to the squirting piston and to the wedge slide for displacing the wedge slide and moving the valve into the closing position as the squirting resistance rises, so as to increase the braking resistance and retard the forward movement of the driving and working pistons to correspond to the increasing resistance set up by the thermoplastic mass as the squirting progresses, and a counterweight operatively connected to the wedge slide and arranged to act in opposition to the adjusting means.

4. In a machine for squirting thermoplastic masses, in combination a driving piston, a squirting piston comprising a hollow outer member operatively connected to said driving piston for actuation by the latter and an inner member slidable in the outer member and arranged to protrude from the outer member so as to act on the mass to be squirted, the end of the outer member remote from the protruding end of the inner member being closed so as to form a space above the end of the inner member for containing pressure fluid, a brake arranged for operation by pressure fluid and operatively connected to the driving piston for retarding the motion of the driving piston during the working stroke and adjusting means for said brake comprising a vent valve for permitting the escape of fluid from the brake, a wedge slide operatively connected to the vent valve, adjusting means arranged for operation by.fluid pressure for adjusting the wedge slide and a flexible pipe connected to said space and said adjustingmeans for displacing the wedge slide and moving the valve into the closing position as the squirting pressure increases the pressure of the fluid in the said space and a counterweight operatively connected to the wedge slide and arranged to act in opposition to the adjusting means.

5. In a machine for squirting thermoplastic masses, in combination a driving piston, a squirtingpiston comprising a hollow outer member connected to the driving piston for actuation by the latter and an inner member slidable in the outer member and arranged to protrude from one end of the outer member so as to act on the mass to be squirted, the other end of the outer member being closed so as to form a space above the end of the inner member for containing a pressure fluid, a brake operatively connected to the driving piston for retarding the motion of the driving piston during the working stroke,

fluid-operated adjusting means for varying the braking resistance, a conduit connected to said adjusting means and to the said space in the outer member of the squirting piston for transmitting the fluid pressure in said space to the adjusting means so as to actuate the adjusting means to increase the braking resistance as the squirting resistance rises and retard the forward movement of the driving and squirting pistons to correspond to the increasing resistance set up by the thermoplastic mass as the-squirting progresses.

6. In a machine for squirting thermoplastic masses-in combination a driving piston, a squirting piston comprising a hollow outer member connected to the driving piston for actuation by the latter and an inner member slidable in the 'outer member and arranged to protrude from one end of the outer member so as to act on the mass to be squirted, the other end of the outer of the squirting piston for transmitting the fluid pressure in said space to the adjusting means so as to actuate the adjusting means to increase the braking resistance as the squirting resistance rises and retard the forward movement of the driving and squirting pistons to correspond to the increasing resistance set up by the thermoplastic mass as the squirting progresses.

7. In a machine for squirting thermoplastic masses, in combination a driving piston, a squirting piston comprising a hollow outer member connected-to the driving piston for actuation by the latter and an inner member slidable in the outer member and arranged to protrude from one nd of the outer member so as to act on the mass to be squirted, the other end. of the outer member means for said wedge slide and a flexible pipe connected to the said space and said adjusting means for displacing the wedge slide and moving the valve .into the closing position as the squirtrespect to the other, the wedge slide having gear teeth thereon meshing with the said gear wheel.

10'. In a machine for squirting thermoplastic masses, the combination as set forth in claim 1 with a hydraulic brake operatively connected to the driving piston for braking the latter at the end of its return movement.

11. In a machine for squirting thermoplastic masses, in combination, a compressed air operated driving piston, a squirting piston, a toggle interposed between said driving and squirting pistons for establishing a driving connection between them, the linkage of saidtoggle being arranged to transmit the motion of the driving piston so that the squirting piston travels forward quickly at the commencement of the forward motion of the driving piston but slows down as the said forward motion progresses. a

.mould, a rocker lever, a guide lever for the toggle tween them, the linkage of said toggle being arranged to transmit the'motion of the driving piston so that the squirting piston travels forward quickly at the commencement of the forward motion of the driving piston but slows down as the said forward motion progresses, a mould, a rocker lever, a guide lever for the toggle pivoted on the rocker lever and a closing lever arranged to bear on the mould and operatively connected to the rocker lever, saidclosing lever havin its fulcrum so located that'it transmits the tension acting in the guide lever to the mould as a mag nified compressive force for maintaining the mould closed during the squirting operation.

13. In a machine for squirting thermoplastic masses, in combination a driving piston, a squirting piston operatively connected to said driving piston for actuation by the driving piston, a fluid pressure brake operatively connected to the driving pressure increases the pressure in the said space.

8. In a machine for squirting thermoplastic masses, the combination as set forth in claim 3 with a snail plate having a. spiral track thereon wheel thereon and adjustable angularly one with ing piston for retarding the motion of the driving piston during the working stroke, a circulation pipe for said brake having a control valve therein for permitting the escape of fluid into the circulation pipe to reduce the braking action, adjusting means for said valve including a wedge slide and a pressure responsive device connected ing piston comprising a hollow outer member operatively connected to said driving piston for actuation by the latter and an inner member slidable in the outer member and arranged to protrude from the outer member so as to act on the mass to be squirted, the end of .the outer member remote from the protruding end of the inner member being closed so as to form a space above the end of the inner member for containing pressure fluid, a brake arranged for operation by justing means for said brake comprising a vent.

valve for permitting the escape ot fluid from the brake, a wedge slide operatively connected to the vent valve, adjusting means arranged for operation by flui pressure for adjusting the wedge slide and a flexible pipe connected to said space and said adjusting means for displacing the wedge slide and moving the valve into the closing position as the squirting pressure increases the pressure of the fluid in the saidspace.

15. In a machine for squirting thermoplastic masses, the combination as set forth in claim 4 with a snail plate having a spiral track thereon and a tension member passed around said spiral track for supporting the counterweight so asto increase the force exerted by the counterweight on the adjusting means as the wedge slide is displaced to move the valve towards the closing position. a

16. In a machine for squirting thermoplastic masses, the combination as set forth in claim 4 with a shaft having a snail plate and a gear wheel thereon and adjustable angularly one with respect to the other, the wedge slide having gear teeth thereon meshing with the said gear wheel.

EMJLHEMIPEL. 

